Adds folder sensor

.coveragerc

@@ -552,6 +552,7 @@ omit =
     homeassistant/components/sensor/fedex.py
     homeassistant/components/sensor/fitbit.py
     homeassistant/components/sensor/fixer.py
+    homeassistant/components/sensor/folder.py
     homeassistant/components/sensor/fritzbox_callmonitor.py
     homeassistant/components/sensor/fritzbox_netmonitor.py
     homeassistant/components/sensor/gearbest.py

homeassistant/components/sensor/folder.py

@@ -0,0 +1,108 @@
+"""
+Sensor for monitoring the contents of a folder.
+
+For more details about this platform, refer to the documentation at
+https://home-assistant.io/components/sensor.folder/
+"""
+from datetime import timedelta
+import glob
+import logging
+import os
+
+import voluptuous as vol
+
+from homeassistant.helpers.entity import Entity
+import homeassistant.helpers.config_validation as cv
+from homeassistant.components.sensor import PLATFORM_SCHEMA
+
+_LOGGER = logging.getLogger(__name__)
+
+CONF_FOLDER_PATHS = 'folder'
+CONF_FILTER = 'filter'
+DEFAULT_FILTER = '*'
+
+SCAN_INTERVAL = timedelta(seconds=1)
+
+PLATFORM_SCHEMA = PLATFORM_SCHEMA.extend({
+    vol.Required(CONF_FOLDER_PATHS): cv.isdir,
+    vol.Optional(CONF_FILTER, default=DEFAULT_FILTER): cv.string,
+})
+
+
+def get_files_list(folder_path, filter_term):
+    """Return the list of files, applying filter."""
+    query = folder_path + filter_term
+    files_list = glob.glob(query)
+    return files_list
+
+
+def get_size(files_list):
+    """Return the sum of the size in bytes of files in the list."""
+    size_list = [os.stat(f).st_size for f in files_list]
+    return sum(size_list)
+
+
+def setup_platform(hass, config, add_devices, discovery_info=None):
+    """Set up the folder sensor."""
+    path = config.get(CONF_FOLDER_PATHS)
+
+    if not hass.config.is_allowed_path(path):
+        _LOGGER.error("folder %s is not valid or allowed", path)
+    else:
+        folder = Folder(path, config.get(CONF_FILTER))
+        add_devices([folder], True)
+
+
+class Folder(Entity):
+    """Representation of a folder."""
+
+    ICON = 'mdi:folder'
+
+    def __init__(self, folder_path, filter_term):
+        """Initialize the data object."""
+        folder_path = os.path.join(folder_path, '')  # If no trailing / add it
+        self._folder_path = folder_path   # Need to check its a valid path
+        self._filter_term = filter_term
+        self._number_of_files = None
+        self._size = None
+        self._name = os.path.split(os.path.split(folder_path)[0])[1]
+        self._unit_of_measurement = 'MB'
+
+    def update(self):
+        """Update the sensor."""
+        files_list = get_files_list(self._folder_path, self._filter_term)
+        self._number_of_files = len(files_list)
+        self._size = get_size(files_list)
+
+    @property
+    def name(self):
+        """Return the name of the sensor."""
+        return self._name
+
+    @property
+    def state(self):
+        """Return the state of the sensor."""
+        decimals = 2
+        size_mb = round(self._size/1e6, decimals)
+        return size_mb
+
+    @property
+    def icon(self):
+        """Icon to use in the frontend, if any."""
+        return self.ICON
+
+    @property
+    def device_state_attributes(self):
+        """Return other details about the sensor state."""
+        attr = {
+            'path': self._folder_path,
+            'filter': self._filter_term,
+            'number_of_files': self._number_of_files,
+            'bytes': self._size,
+            }
+        return attr
+
+    @property
+    def unit_of_measurement(self):
+        """Return the unit of measurement of this entity, if any."""
+        return self._unit_of_measurement

tests/components/sensor/test_folder.py

@@ -0,0 +1,64 @@
+"""The tests for the folder sensor."""
+import unittest
+import os
+
+from homeassistant.components.sensor.folder import CONF_FOLDER_PATHS
+from homeassistant.setup import setup_component
+from tests.common import get_test_home_assistant
+
+
+CWD = os.path.join(os.path.dirname(__file__))
+TEST_FOLDER = 'test_folder'
+TEST_DIR = os.path.join(CWD, TEST_FOLDER)
+TEST_TXT = 'mock_test_folder.txt'
+TEST_FILE = os.path.join(TEST_DIR, TEST_TXT)
+
+
+def create_file(path):
+    """Create a test file."""
+    with open(path, 'w') as test_file:
+        test_file.write("test")
+
+
+class TestFolderSensor(unittest.TestCase):
+    """Test the filesize sensor."""
+
+    def setup_method(self, method):
+        """Set up things to be run when tests are started."""
+        self.hass = get_test_home_assistant()
+        if not os.path.isdir(TEST_DIR):
+            os.mkdir(TEST_DIR)
+        self.hass.config.whitelist_external_dirs = set((TEST_DIR))
+
+    def teardown_method(self, method):
+        """Stop everything that was started."""
+        if os.path.isfile(TEST_FILE):
+            os.remove(TEST_FILE)
+            os.rmdir(TEST_DIR)
+        self.hass.stop()
+
+    def test_invalid_path(self):
+        """Test that an invalid path is caught."""
+        config = {
+            'sensor': {
+                'platform': 'folder',
+                CONF_FOLDER_PATHS: 'invalid_path'}
+        }
+        self.assertTrue(
+            setup_component(self.hass, 'sensor', config))
+        assert len(self.hass.states.entity_ids()) == 0
+
+    def test_valid_path(self):
+        """Test for a valid path."""
+        create_file(TEST_FILE)
+        config = {
+            'sensor': {
+                'platform': 'folder',
+                CONF_FOLDER_PATHS: TEST_DIR}
+        }
+        self.assertTrue(
+            setup_component(self.hass, 'sensor', config))
+        assert len(self.hass.states.entity_ids()) == 1
+        state = self.hass.states.get('sensor.test_folder')
+        assert state.state == '0.0'
+        assert state.attributes.get('number_of_files') == 1